This invention concerns a panel fitting device, i.e. a device suitable for fitting and replacing corrugated synthetic resin plates to be used for the roof, wall and gable of a hothouse.
Generally a hothouse is used to cultivate vegetables, fruits and flowers and to breed fish, and the hothouses popularly used are the glass house which uses transparent or semitransparent glass plates on the roof, wall and gable and the vinyl house which is covered by transparent or semitransparent vinyl sheet material.
A glass house has various shortcomings, however. The vegetables and fruits are poor in quality as compared with natural ones (e.g. pear, tomato, etc. are not well colored) for example, due to the low transmission (less than 90%) of sun light, especially ultraviolet rays. Glass is easy to break when an external force such as human body weight is imposed or when rocks, roof tiles, trees, etc. blown by strong wind hit the glass. Also the broken pieces of glass drop into the soil in the hothouse, and are very difficult to remove. The price of glass itself is high and the construction cost will be very high when it is used all around the hothouse. Glass plate is limited in size and cannot be used for a hothouse with large frontage and many fastening parts are required.
The vinyl house can be more easily constructed and is cheaper than the glass house, but it too has shortcomings. Because of its thinness, it has poor durability; it is easily broken by external forces such as wind and rain and it cannot withstand human body weight. Vinyl also has poorer light transmission than glass and when it becomes dirty, it cannot be cleaned easily. It is difficult to stretch and set the vinyl sheet; many fitting parts are required that increase the cost; it is very difficult to replace or maintain because the sheet is easy to break; and sunlight transmission decreases as it becomes dirty.
For the above reasons, recently a hothouse using corrugated panels made of acrylic resin only has been developed and is being used increasingly in place of the glass house and vinyl house.
The acrylic panel is superior in transparency, ultraviolet ray transmission, weather-proofing, and heat reserving quality and is an ideal covering material for the hothouse or similar house. The acrylic panel has the following advantages: (1) since there is no loss in diffusion, reflection and absorption of light and the light transmission is 93% or more, plant disease is prevented and fruits are well colored, (2) no separation of resin and fiber or cloudiness (whitening) which are often found in composite material and no penetration of rain water into the interior or contamination takes place, (3) feating excellent tensile strength and breaking strength and having a usage life of 20 years or more, it withstands typhoon or strong winds and other external forces, and therefore there is little need for maintenance or replacement, (4) the house can be made airtight and energy savings can be expected, (5) various sizes and specifications are available, construction is easy, and large size houses can be built, and (6) construction cost can be reduced because it is cheaper than glass.
Despite the fact that the acrylic panel has such advantages as described above, it has a serious shortcoming as described below because it must be installed by means of hook bolts inserted into holes drilled in the panel and no other better way has so far been developed.
When the transparent corrugated acrylic panels are used on the roof, wall and gable of a hothouse, they are placed one upon another as shown in FIG. 1. The lower acrylic panel at 1 and 2 is placed on a pipe or C-shaped channel 23 which is part of the framework of the hothouse, and the upper acrylic panel 2 is plced upon the lower panel with an unwoven acrylic packing 24 in between, and then, a hook bolt 25 is inserted into the bolt hole drilled in the upper acrylic panel 2. The hook 26 of the hook bolt 25 is hitched in the bent part of the pipe or C-shaped channel 23 and tightened with the nut 29 under which the rubber packing 27 and washer 28 are placed. The top end of the lower acrylic panel 1 is caught rather loosely between the C-shaped channel 23 and the upper acrylic panel 2 so that it can expand or contract in summer and winter.
However, one of the serious shortcomings of the above method is that the bolt hole must be drilled in the upper acrylic panel 2, and in addition, it has also the following shortcomings. (A) Since the acrylic panel 2 is rigid, cracks occur around the hole when the bolt hole is drilled with a tool and the cracks expand all over the panel, (B) there is a lot of work because multiple holes must be drilled in the upper panel 2 and utmost care must be exercised so that the cracks will not occur, (C) even if the drilling work is safely done, the stress will be concentrated around the bolt hole during long usage due to typhoon or other external forces such as a man stepping on the panels, thus causing complicated cracks around the bolt hole and finally replacement will be necessary, (D) the parts cost is very high because many parts such as hook bolts 25 and packings 27 must be used in the multiple holes, (E) two workers are required, one for hitching the C-shaped channel 23 with the hook bolt 25 and another for tightening the nut 29 thus increasing the labor cost and also the fitting is difficult work, (F) if the rubber packing 27 is worn, rain water or cold air comes into the hothouse and its heat reserving quality and airtightness will be impaired.